Reflector and backlight device

ABSTRACT

A back light device realizing improvement in hotspots and bright line in the region of light incidence and of darkness arising in between light sources is provided by forming the reflective surface of the reflector as a structured face comprising an iteration of prism elements of trapezoidal section.

This is a National Phase Application in the United States ofInternational Patent Application No. PCT/JP2005/000344 filed Jan. 14,2005, which claims priority on Japanese Patent Application No.2004-007950, filed Jan. 15, 2004 The entire disclosures of the abovepatent applications are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a reflector and a backlight deviceemploying this reflector.

BACKGROUND ART

The technology conventionally provided for illuminating a liquid crystaldisplay device such as a mobile telephone or the like consists of alight guide plate that guides light emitted from a light source to aliquid crystal display device and a backlight device providing thislight guide plate, that illuminates a liquid crystal display device fromthe rear.

FIG. 1 provides a perspective view, showing the external appearance of aconventional light guide plate. Light sources of light emitting diodes 2are shown in FIGS. 1( a), (b) and (c). Here, the light guide plate 1 ismade of a transparent material such as PMMA or polycarbonate or thelike, and has a substantially flat, planar form. The light guide platehas an upper face constituting an exit face 3 and a lower faceconstituting a reflective face 4, while one of the side faces providesan entry face 5. The reflective face 4 has reflective elements 6 formedthereon that reflect light entering from the entry face 5 toward theexit face 3.

Light emitted from the light sources 2 enters the light guide plate 1from the entry face 5 and is reflected at the reflective elements 6formed on the reflective face 4, being deflected in the direction of theexit face 3, before being emitted from the exit face 3. The light guideplate 1 in which light entering from the entry face 5 comprising one ofthe side faces is emitted from the exit face 3 comprising the main face,is known as a side edge type and is widely used for mobile telephonesand the like.

FIG. 2 provides a cross-sectional view depicting the usage of aconventional light guide plate and backlight device. The light guideplate 1 is disposed directly under the liquid crystal display device 7,such that the entry face 3 opposes the lower face 9 of the liquidcrystal display device 7 with the optical sheet 8 disposed between thatexit face 3 and lower face 9. Light emitted from the light emittingdiodes 2 is incident to the light guide plate 1 from the entry face 5.

This light entering the light guide plate 1 from the entry face 5 isdeflected at the reflective elements 6 formed on the reflective face 5that opposes the exit face 3, reflecting upward in the direction of theliquid crystal display device 7 and exiting from the exit face 3.

Light exiting from the exit surface 3 of the light guide plate 1 entersthe lower face 9 of the liquid crystal display device 7 via the opticalsheet 8. This optical sheet 8 points the light exiting from the lightguide plate 1 upward in the direction of the liquid crystal displaydevice 7 such that the light enters the lower surface 9 of the liquidcrystal display device 7 vertically.

A reflector 10 that reflects light emitted from the reflective face 4 isdisposed at the side closer to the reflective face 4 of the light guideplate 1. The reflective surface of the conventional reflector 10 is apure, mirror surface.

DISCLOSURE OF THE INVENTION

In the conventional art, light emitted from the light sources 2 entersthe light guide plate 1 from the entry face 5, however light rays fromthe diode point light sources spread out in a fan shape as they areguided inside the light guide plate 1 and darkness arises between thelight sources 2 in the vicinity of the entry face 5 of the light guideplate 1 due to these point light sources.

Light from the light sources 2 easily gives rise to pulsating shades oflight or eyeball like glows called hotspots or bright line in the regionof the entry face 5 due to the intensity of the light emitting diodelight rays.

Accordingly, while a process of trial and error has been applied to thedesign of the form of the light emitting diodes 6, as light raysreflected and deflected are emitted directly from the exit face 3 of thelight guide plate 1 and pass via the optical sheet 8 while traveling tothe liquid crystal display device 7, a problem arises, as shown in FIG.3, with the occurrence of bright hotspots 11, bright line 12 anddarkness 13 due to insufficient distribution of light rays between thelight sources 2.

The present invention provides a reflector and a backlight deviceemploying this reflector that solves these problems.

In order to solve the above problems, in the reflector related to thepresent invention the reflection face includes a structured facestructured from an iteration of prism elements having a trapezoidalsection. It is preferable that the height of the trapezoidal section ofthe prism elements be uniform. It is preferable that a metallic layer ofsilver, a silver alloy or aluminum or the like be formed on the surfaceof the structured face of the reflector in order to increase thereflectivity. Further, it is preferable that a protective layer of atransparent metallic oxide material or resin be formed on the surface ofthe metallic layer to provide improved durability.

The backlight device related to the present invention is a backlightdevice having a light guide plate for propagating, reflecting anddiffusing light, disposed at the rear surface side of a display device,a light source disposed at the end at at least one side of the lightguide plate, and a reflector for reflecting light from the light guideplate disposed at the lower face of the light guide plate, wherein thereflective surface of the reflector includes a structured facestructured from an iteration of prism elements having a trapezoidalsection.

The height of the sections of the prism elements should be preferablyuniform. Moreover, this height of the sections of the prism elementsshould preferably be progressively decreasing. It is preferable that thecrest line direction of the prism elements be a direction vertical tothe surface closer to the light source of the light guide plate. It isfurther preferable that the light guide plate provides reflectiveelements formed integrally with the surface thereof adjacent to theliquid crystal display device, and that light rays be emitted from thesereflective elements in the direction of a reflector adjacent to thelight guide plate face opposing the side of the light guide plate closerto the liquid crystal display devices.

Moreover, it is preferable that in order to further improve the problemsof hotspots or bright line, or of darkness that occurs between the lightsources, that an anisotropic diffusion pattern be formed on the face ofthe light guide plate opposing the face on which the reflective elementsare integrally formed. Again, it is preferable that this anisotropicdiffusion pattern diffuses the greater part of light in the directionbetween the light sources, and the lesser part of the light in thedirection of a anti-entry part. Further, it is preferable that theanisotropic diffusion pattern be an uneven pattern formed from a surfacerelief hologram.

Because the reflective surface of the reflector is changed from what wassimply a mirror surface in the conventional art to a structured facestructured from an iteration of prism elements having a trapezoidalsection, light emitted from the reflective surface of the light guideplate can be reflected in a direction different to the direction ofreflection from the purely mirror surface. This reflected light reentersthe light guide plate, and finally enters the liquid crystal displaydevice via the optical sheet, however, as light reflected in a directiondifferent to the direction of reflection of the purely mirror surface isadded, an improvement can be realized in the problems of darknessoccurring between the light sources and of hotspots and bright lineoccurring in the region of light input affecting the conventionaltechnology.

Thus, a backlight device is realized having a decrease in darknessoccurring between the light sources and of hotspots and bright lineoccurring in the region of light input, that realizes less unevennessand improved uniformity of luminance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a light guide plate, FIG. 1( a) providing a plan view, FIG.1( b) providing a front view and FIG. 1( c) providing a perspectiveview;

FIG. 2 shows the structure of a conventional backlight device;

FIG. 3 shows hotspots or bright line occurring in the light input regionand darkness occurring between the light sources in a conventionalbacklight device;

FIG. 4 shows an embodiment of a reflector according to the presentinvention;

FIG. 5 shows an embodiment of a reflector according to the presentinvention;

FIG. 6 shows an embodiment of a reflector according to the presentinvention;

FIG. 7 shows an embodiment of a reflector according to the presentinvention;

FIG. 8 shows an embodiment of a backlight device according to thepresent invention;

FIG. 9 shows the backlight device, FIG. 9( a) providing a plan view,FIG. 9( b) providing a front view and FIG. 9( c) providing a perspectiveview;

FIG. 10 shows a cross-section of the light guide plate;

FIG. 11 shows the traveling direction of a light ray within the lightguide plate;

FIG. 12 shows the anisotropic diffusion hologram pattern integrallyformed with the light guide plate;

FIG. 13 shows the anisotropic diffusion hologram pattern magnified 200times;

FIG. 14 is an explanatory drawing that illustrates the properties of thehologram, FIG. 14( a) providing a plan view showing the strength ofangle dependency of light emitted from the points P1, P2 and P3 of theexit face 12 of the light guide plate and FIG. 14( b) providing aperspective view showing, three dimensionally, the strength distributionof light emitted from the point P2 of the exit surface 11 of the lightguide plate 10;

FIG. 15 illustrates the production of the hologram of this embodiment;

FIG. 16 is a perspective view showing the structure of the device usedfor producing the master hologram;

FIG. 17 shows a part of the backlight device formed of the light guideplate and the optical sheet; and

FIG. 18 shows the optical sheet.

BEST MODE FOR CARRYING OUT THE INVENTION

The reflector and backlight device related to the present invention willnow be described with reference to the drawings.

For simplicity, in these drawings, like reference numerals identify likeelements. Further, the drawings of the embodiments of the presentinvention are provided in order to illustrate the content of theinvention but are not intended to accurately reflect the relativeproportions of each of the parts.

To enable ease in referencing, an orthogonal xyz coordinate system isset over some of the drawings. The x-axis and the y-axis are set in thetwo regions of the upper face and the lower face of the light guideplate in the direction of travel of light in the light guide plate, andthe z-axis is set in the direction of the normal to the exit face.Further, the positive and negative directions of the z-axis are termedupwards and downwards.

FIG. 4 shows an embodiment of a reflector according to the presentinvention. FIG. 4( a) provides a cross-sectional view and FIG. 4( b) aperspective view. With this embodiment, trapezoidal section prismelements are formed as a continuum with no gap opening between one prismelement and another on the reflective surface of the reflector. As shownin FIG. 4( b), the height of the trapezoidal section of each prismelement should be uniform. The length of the base of each trapezoid,that is to say, the repetition cycle of the prism elements shouldpreferably be 1-200 μm, and more preferably still 10-100 μm. If this isless than 1 μm a spectral effect due to diffraction intensifies leadingto a deterioration in the display capabilities of the liquid crystaldisplay device while if it exceeds 200 μm the repetitive structure isvisible from the liquid crystal display side. The angle formed by theoblique side of the trapezoid and the base should preferably be 20-70°and more preferably still 35-55°.

If that angle is less than 20° or greater than 70° there is adeterioration in the effect of improving the problems of hotspots orbright line in the light input region or of darkness between the lightsources. The left and right base angles of each trapezoidal section maybe even or different. The ratio of the length of the upper side to thelength of the base (the repetition cycle of the prism elements) shouldpreferably be 0.05-0.5 and more preferably still 0.1-0.3. If this isbelow 0.05 luminance deteriorates while if it exceeds 0.5 there is adeterioration in the effect of improving the problems of hotspots orbright line in the light input region or of darkness between the lightsources. Further, the trapezoidal section of each prism element may bethe same or different to the others.

Where the trapezoidal section is triangular shaped damage is easilysustained at the apex part leading to a defect and deterioration indisplay quality, but providing the trapezoid is advantageous by makingsuch defects less likely to occur.

This structure of an iteration of prism elements of a trapezoidalsection as shown in FIG. 4, can be obtained by applying a suitablethickness of ultraviolet cured resin on for example PET film,irradiating from the PET film side while pressing a mold of theappropriate form to the other side, then removal from the mold afterhardening the ultraviolet cured resin.

It is preferable that a metallic layer of silver, a silver alloy oraluminum or the like be formed on the surface of the structured faceformed of an iteration of prism elements of a trapezoidal section, inorder to increase the reflectivity, silver or a silver alloy beingespecially preferable for this. The metallic layer can be formed by adeposition method or a sputtering method. It is preferable that themetallic layer be formed following the prism shape of the structuredface. If the structured layer is made flat, there is a deterioration inthe effect of improving the problems of hotspots or bright line in thelight input region or of darkness between the light sources. Further, ananchor layer should be formed between the structured face and themetallic layer to provide improved adhesiveness.

Further, it is preferable that a protective layer of a transparentmetallic oxide material or resin be formed on the surface of themetallic layer to provide improved durability. This protective layer maybe formed following the prism shaped form of the structured face or soas to make the structured face flat, however if this protective layer isformed following the prism shaped form, the effect of improving theproblems of hotspots or bright line in the light input region or ofdarkness between the light sources is strongest, therefore this is morepreferable.

The rate of reflectivity of the reflector should preferably be not lessthan 75% and not more than 80%. If this is less than 75% there is adecrease in the luminance of the backlight, also bright line becomesmore prominent in the region of light entry.

FIG. 5 shows a second embodiment of a reflector according to the presentinvention, FIG. 5( a) providing a cross-sectional view and FIG. 5( b) aperspective view. For this embodiment trapezoidal section prism elementsare formed as a continuum with a gap opening between one prism elementand another on the reflective surface of the reflector. As shown in FIG.5( b), the height of the trapezoidal section of each prism elementshould be uniform. The repetition cycle of the prism element shouldpreferably be 1-200 μm, and more preferably still 10-100 μm.

If this is less than 1 μm a spectral effect due to diffractionintensifies leading to a deterioration in the display capabilities ofthe liquid crystal display device while if it exceeds 200 μm therepetitive structure is visible from the side of liquid crystal display.The angle formed by the oblique side of the trapezoid and the baseshould preferably be 20-70° and more preferably still 35-55°. If thatangle is less than 20° or greater than 70° there is a deterioration inthe effect of improving the problems of hotspots or bright line in thelight input region or of darkness between the light sources.

The left and right base angles of each trapezoidal section may be evenor different. The sum of the length of the upper side and the length ofthe gap between prism elements should preferably be a ratio in the rangeof 0.05-0.5 in relation to the repetition cycle of the prism elementsand more preferably still 0.1-0.3. If this is below 0.05 luminancedeteriorates while if it exceeds 0.5 there is a deterioration in theeffect of improving the problems of hotspots or bright line in the lightinput region or of darkness between the light sources. Further, thetrapezoidal section of each prism element may be the same or differentto the others.

Where the trapezoidal section is triangular shaped damage is easilysustained at the apex part leading to a defect and deterioration indisplay quality, but providing the trapezoidal section is advantageousby making such defects less likely to occur.

FIG. 6 and FIG. 7 show a reflector according to a third embodiment ofthe present invention. For this embodiment the height of the trapezoidalsection of the reflective surface of the reflector is formed by aniteration of prism elements, the height of triangular section of theprism elements decreases progressively. It is suitable if there is nogap between prism elements as shown in FIG. 6( a) or if there is a gapas shown in FIG. 6( b). Further the repetitive arrangement toward thecrest line direction of the prism elements may have a single prismelement arrangement or a plurality of the prism elements arranged inrepetition as shown in FIG. 7.

Moreover, in the case of this embodiment, the preferable ranges for suchthings as the length of the base of the trapezoidal section, therepetition cycle of the prism elements, the angle of the oblique side ofthe trapezoidal section and the base, the ratio of the length of theupper side of the trapezoidal section to the length of the base, and theratio of the sum of the length of the gaps between prism elements andthe length of the upper side of the trapezoidal section are the same asthe respective values applying for the first and second embodiments.

Further, in the case of the second and third embodiments also, in thesame way as applies with respect to the first embodiment, the structuredface can be obtained by applying a suitable thickness of ultravioletcured resin on for example PET film, irradiating from the PET film sidewhile pressing a mold of the appropriate form to the other side, thenremoval from the mold after hardening the ultraviolet cured resin.

Again, it is preferable that a metallic layer of silver, a silver alloyor aluminum or the like be formed on the surface of the structured faceformed of an iteration of prism elements of a trapezoidal section inorder to increase the reflectivity, silver or a silver alloy beingespecially preferable for this. The metallic layer can be formed by adeposition method or a sputtering method. It is preferable that themetallic layer be formed following the prism shape of the structuredface. If the structured layer is made flat, there is a deterioration inthe effect of improving the problems of hotspots or bright line in thelight input region or of darkness between the light sources. Further, ananchor layer should be formed between the structured face and themetallic layer to provide improved adhesiveness.

Further, it is preferable that a protective layer of a transparentmetallic oxide material or resin be formed on the surface of themetallic layer to provide improved durability. This protective layer maybe formed following the prism shaped form of the structured face or soas to make the structured face flat, however if this protective layer isformed following the prism shaped form, the effect of improving theproblems of hotspots or bright line in the light input region or ofdarkness between the light sources is strongest, therefore this is morepreferable.

FIG. 8 shows an embodiment of a backlight device according to thepresent invention. This backlight device in FIG. 8 has the samecross-section as the backlight device of the figure described withrelation to conventional technology.

The light guide plate 1 provides reflective elements 6 and an opticalsheet 8 that is a prism sheet or the like, disposed between the lightguide plate 1 and liquid crystal display elements 7. On the other hand,at the side opposite that side at which the optical sheet 8 of the lightguide plate 1 is disposed, a reflector 10, having the structured face ofthis invention is provided. In FIG. 8 the reflective elements 6 of thelight guide plate are disposed on the exit face 3, however these mayalso be provided to on the opposing face adjacent to the reflector 10.

FIG. 9 shows the backlight device according to this embodiment, FIG. 9(a) providing a plan view, FIG. 9( b) providing a front view and FIG. 9(c) providing a perspective view. In those figures the light emittingdiodes 2 light sources are shown.

As shown in FIG. 11, in the case of this embodiment the reflectiveelements 6 are integratedly formed with the exit face 3 at that side ofthe light guide plate 1 closer to the liquid crystal display device 7.Light rays 100 entering the light guide plate 1 from the light emittingdiodes 2 in the xy plane are reflected and deflected in the z axialdirection, a part of this light passing the face 14 opposing the entryface 3 and reaching the reflective 10.

It is suitable for this face 14 opposing the exit face 3 of the lightguide plate 1 to be a mirror surface or a rough surface, but in the caseof this embodiment a diffusion pattern integrated layer 18 capable ofanisotropically diffusing light is integratedly formed with this face.The light guide plate 1 is comprised of a transparent material having aconstant refractive index such as PMMA, polyolefine or polycarbonate,being of a substantially planar form having a substantially rectangularshaped upper face and lower face.

Referring to the above coordinate axis, the light guide plate 1 isformed with the upper face and lower face substantially parallel to thexy plane, these faces comprising respectively the exit face 3 andanisotropic diffusion pattern integrated layer 18, while between theexit face 3 and anisotropic diffusion pattern integrated layer 18, beingthe end face that enters light rays, is the entry face 5.

The reflective elements 6 are integratedly formed on the exit face 3.These reflective elements 6 discharge the role of reflecting the lightentering from the entry face 5 and deflecting the light in the directionof the anisotropic diffusion pattern integrated layer 18. The reflectiveelements 6 are formed continuously or discontinuously from one of theside faces of the light guide plate 1 to the other, and a greater partof these elements are used for reflecting light. Accordingly, the exitface 3 on which are formed the reflective elements 6 of this embodimenthave a high degree of efficiency in reflecting incoming light in thedirection of the anisotropic diffusion pattern integrated layer 18 andimprove the efficiency of usage of light by the light guide plate 1.

A hologram having anisotropic properties (anisotropic diffusion pattern)is formed on the anisotropic diffusion pattern integrated layer 18. Thishologram is termed a surface relief hologram to distinguish it from athree dimensionally formed hologram. The hologram diffuses light emittedfrom the anisotropic diffusion pattern integrated layer 18 substantiallyin the direction between the light sources 2 and passes the light. Lightrays that travel to the anti-entry face 15, that is the face opposingthe entry face 5 are arranged so as to be diffused to a lesser degree.Light reflected at the reflective elements 6 is diffused substantiallyby the hologram in the direction between the light sources 2 in order tocompensate for insufficient quantity of light rays occurring between thelight sources 2, and light that is diffused in a substantiallyelliptical form is emitted from the anisotropic diffusion patternintegrated layer 18.

The light guide plate 1 having the form as described above can beproduced by extrusion molding processes in a mold using a material suchas PMMA, polyolefine or polycarbonate.

FIG. 10 shows the dimensions of each part of the light guide plate.

The distance a between the exit face 3 and anisotropic diffusion patternintegrated layer 18 is generally determined by the type of the lightsources 2, however, this distance should be within the range from0.3-3.0 mm, preferably 0.4-1.0 mm and more preferably still 0.5-0.8 mm.The angle θ1 formed between the first face 6 ₁ of the reflectiveelements 6 and the exit face 3 should be between 0.2-5°, preferably0.3-3.0° and more preferably still 0.3-1.50. The angle θ2 between thesecond face 6 ₂ of the reflective elements 6 and the exit face 3 shouldbe not greater than 90°, preferably 30-89° and more preferably still35-89°.

The interval p between neighboring reflective elements 6 should beuniform, and preferably within the range 50-500 μm, more preferably50-250 μm and more preferably still 100-150 μm. Note that if theinterval p is made uniform a moire phenomena arises due to interferencefrom the cell arrangement of the liquid crystal display elements 7,therefore this interval can intentionally be made random.

FIG. 11 shows the traveling direction of a light ray within the lightguide plate.

Light rays 100 incident to the entry face 5 of the light guide plate 1from the light sources 2 travel inside the light guide plate 1repeatedly undergoing total reflection between the anisotropic diffusionpattern integrated layer 18 and the exit face 3 until the angle betweenthe traveling direction of the light and the anisotropic diffusionpattern integrated layer 18 reaches a critical angle.

The first face 6 ₁ of the reflective elements 6 performs the role ofdeflecting light to be reflected in the direction of the anisotropicdiffusion pattern integrated layer 18. Light the traveling direction ofwhich forms a small angle with the exit face 3 entering the entry face 5is deflected in the direction of the anisotropic diffusion patternintegrated layer 18 as it is reflected at the first face 6 ₁ of thereflective elements 6, and when the angle of this traveling light andthe anisotropic diffusion pattern integrated layer 18 exceeds a criticalangle, the light is output from the anisotropic diffusion patternintegrated layer 18.

Here, to the extent that the angle θ1 formed between the first face 6 ₁of the reflective elements 6 and the anisotropic diffusion patternintegrated layer 18 is small, the light is gradually pointed upward dueto reflection at the first face 6 ₁ of the reflective elements 6, thusthe direction of light output from the light guide plate 1 iscollimated. The light thus arranged can be easily managed, but lightextracted from the anisotropic diffusion pattern integrated layer 18 isfurther deflected by the reflective grooves 16 formed on the face of thereflector 10 and the metal deposition layer 17 formed on the face of thereflective grooves 16, and the light rays are reflected in the directionof the light guide plate 1 again.

These light rays are further diffused at the anisotropic diffusionpattern integrated layer 18 and are directed toward the exit face 3. Atthis time, as the traveling direction of the light rays is set to anangle below the angle for total reflection in relation to the faces ofthe anisotropic diffusion pattern integrated layer 18 and the reflectiveelements 6, light reflected from the metal deposition layer 17 and thereflective grooves 16 of the reflector 10 is emitted from the exit face3 of the light guide plate 1. Light rays emitted from the light guideplate 1 undergo a determined deflection at the optical sheet 8 beforeentering the lower face 9 of the liquid crystal display elements 7.

In the light guide plate 1 of this embodiment the shape of thereflective elements 6 employs a V-shaped form as shown in FIG. 11.

The angle between the inclination of the reflective elements 6 and theexit face 3 (θ1) is 0.7°, the reflective elements 6 being disposed fromthe corner part 119 and the intersection of the entry face 5 at aconstant pitch of 120 μm. As shown in FIG. 11 the mold for the lightguide plate 1 is prepared having V shaped grooves such that the inclinedface is directed to face the light sources 2 so that the angle ofinclination brings light from the entry face 5 gradually to an anglebelow that angle for total reflection and the light guide plate isproduced by extrusion processes using the mold.

It is preferable that a pattern that diffuses light the formed on theface 18 that opposes the reflective elements 6. In this case it ispreferable that light is substantially diffused in the direction betweenthe light sources 2 and diffusion in the direction between thereflective entry face 15 and the light sources be smaller, therebyrealizing improved frontal luminance. For the light guide plate 1according to this embodiment, the hologram formed by the anisotropicdiffusion pattern integrated layer 18 diffuses substantially in thedirection between the light sources 2 while the diffusion of light issmaller in the direction between the reflective entry face 15 and thelight sources 2. Further, each of the half value diffusion angles use apattern having 60° in the direction between the light sources and 1° inthe other direction.

FIG. 12 shows the anisotropic diffusion hologram pattern integrallyformed with the light guide plate.

FIG. 13 shows the anisotropic diffusion hologram pattern magnified 200times.

As shown in FIG. 12, the hologram is arranged such that diffusion issubstantial in the direction between the light sources 2 and smaller inthe direction between the reflective entry face 15 and the lightsources.

Of light rays 100 that undergo total reflection and are deflected at theV-shaped reflective elements 6 integratedly formed on the exit face 3, aportion thereof that reach the anisotropic diffusion pattern integratedlayer 18 are reflected to the reflector 10 side of the light guide plate1. When a light ray 100 that has undergone total reflection anddeflection at the V-shaped reflective elements 6 reaches the anisotropicdiffusion pattern integrated layer 18, the angle of total reflection islost as the anisotropic diffusion pattern integrated layer 18 has arough face (see FIG. 11), so a part of the light rays are emitted towardthe reflector 10 side of the light guide plate 1. When these light rays100 are emitted from the light guide plate 1, these light rays areanisotropically diffused due to the diffusion characteristics of thehologram, and the light is diffused substantially in the directionbetween the light sources 2 before reaching the reflector 10.

FIG. 14 is an explanatory drawing illustrating the properties of themaster hologram.

FIG. 14( a) is a plan view showing angle dependence of the luminance oflight emitted from the points P1, P2, P3 of the anisotropic diffusionpattern integrated layer 18. FIG. 14( b) is a perspective view showingin solid form, the strength distribution of light emitted from the pointP2 of the anisotropic diffusion pattern integrated layer 18 of the lightguide plate 1.

Due to the effect of the hologram formed on the anisotropic diffusionpattern integrated layer 18, light emitted from the points P1, P2 and P3of the anisotropic diffusion pattern integrated layer 18 of the lightguide plate 1 diffuses substantially in the direction between the lightsources 2 as shown by the ellipses E1, E2 and E3, while the lightdiffuses less in the direction between the reflective entry face 15 andthe light sources. The ratio of the longitudinal axial direction and theshorter axial direction of the ellipses E1, E2 and E3 that shows thestrength distribution of the diffused light is changeable, but in thecase of this embodiment this ratio is 1:60.

FIG. 15 is a block diagram showing the configuration of the device usedfor forming the master hologram.

The hologram formed by the anisotropic diffusion pattern integratedlayer 18, is a copy of a master hologram and has the same opticalproperties as the master hologram.

The device shown in FIG. 15 has a laser light source 71 for emittinglaser light of a determined wavelength, a mask 72 having an opening offor example a rectangular shape, a mask 73 for passing light only ofdesired regions and a table 75 that supports a photoresist such that aphotoresist is movable in the planar direction.

The laser light source 71 can switch between the red, green and blue(RGB) elements of the laser light and emit the light.

This is because in order to produce a hologram that diffuses the whitelight required for illuminating the liquid crystal display device of forexample a mobile telephone device, it is necessary to expose each of theRGB elements of the laser light to the photoresist 74. Three laser lightsources emit respectively one of the RGB elements, and a switch occursbetween these different light sources as the device is used.

The mask 72 has an opening provided by a rectangular shaped diffuser.Frost glass for example can be used for this diffuser. The dimensions ofthe respective long and short sides of the rectangular shape correspondrespectively to the dimensions of the short and long axes of thesubstantially elliptical speckles formed on the photoresist 74. Notethat the relationship between the long and short sides and the short andlong axes is a mutual relationship of Fourier transformation.

The mask 73 is used such that light is exposed only to the requiredregions of the photoresist 74. The hologram according to this embodimentdoes not expose light at once to all of the photoresist 74, but ratherthe appropriate parts are exposed so that each part obtains the desireddiffusion characteristics. Multiple light exposures are performedrepeatedly to each part until the photoresist 74 has been exposedentirely. This multiple light exposure is performed for each of therespective RGB elements. Once the hologram thus exposed to light isdeveloped the master hologram is obtained.

The photoresist 74 is a thick film uniformly distributed with a highlyphotosensitive body such that extremely weak light can be detected andthe speckles faithfully reproduced.

The supporting base 75 is used to move the photoresist 74 in the planardirection. The table 75 changes the position of light exposure to thephotoresist 74 and adjusts the distance between the masks 72 and 73, andthe photoresist 74 when moving the photoresist 74.

FIG. 16 is a perspective view showing the configuration of the deviceused for forming the master hologram.

The masks 81 and 82 are equivalent to the mask 72 having the rectangularshaped opening shown in FIG. 15. The mask 81 has a slit 81 a. The shortside of the rectangular shaped opening is determined by the width ofthis slit. The mask 82 has a triangular shaped opening 82 a. The longside of the rectangular shaped opening is determined by the maximumlength in the longitudinal direction of the region of the slit 82 a ofthe triangular shaped opening 82 which passes light passing the slit 81a of the mask 81. The masks 81 and 82 diffuse light passed by a diffusernot shown in the drawing.

The mask 83 equates to the mask 73 shown in FIG. 15. This mask 83 has arectangular shaped opening 83 a. The regions of the photoresist 84 thatare exposed to light are limited to those parts to which light passingthis rectangular shaped opening 83 a reach. The entire face of thephotoresist 84 can be exposed to light by changing these parts of thephotoresist 84 and performing multiple exposures.

A master hologram is obtained when a photoresist is exposed to lightusing the devices shown in FIG. 15 and FIG. 16 and developed. A masterhologram produced in this way is unevenly transferred to partscorresponding to the exit face of the mold used for producing the lightguide plate. This mold to which the master hologram has been transferredis then used to produce the light guide plate by injection molding andthe hologram can be integratedly formed on the lower face of the lightguide plate.

FIG. 17 shows a part of the backlight device formed by the light guideplate and optical sheet.

In this backlight device comprising the light guide plate 1 and theoptical sheet 8 light emitted from the exit face 3 of the light guideplate 1 includes lights L₁ and L₂, being light elements which form asmall angle with the exit face 3. The optical sheet 8 has a flat upperface 51 and a prism shaped lower face 52. When the lights L₁ and L₂ thatform a small angle with the exit face 3 of the light guide plate 1 enterfrom this lower face 52, the angle is changed so as to become asubstantial angle with the upper face 51 and the lights are emitted (L₁′and L₂′). In this way the optical sheet 8 improves the frontal strengthof light output to the liquid crystal display elements 7.

FIG. 18 shows the optical sheet.

This optical sheet is made of a transparent material such as for examplePMMA, polyolifine, polycarbonate or a photoresistant resin. Reflectivegrooves 53 that form a continuous prism shaped construction are disposedon the lower face 52 opposing the upper face 51. This optical sheet 8 isdisposed above the exit face 3 of the light guide plate 1.

An example of a backlight device applying the present invention will nowbe described. In the following examples the following configuration isused throughout. This configuration is described with reference to FIG.8.

Four NSCW335's by Nichia were used for the light sources. The lightguide plate 1 was of polycarbonate, the entry face 5 having a length of40 mm in the planar direction, 50 mm in the perpendicular direction andwas of 0.7 mm thickness. The reflective elements 6 were formed with thevalues for those items shown in FIG. 10 being θ1=1.5°, θ2=35° and p=150μm. A hologram pattern, formed by an anisotropic diffusion patternintegrated layer 18 was formed on that face of the light guide plate 1at the opposite side to that on which the reflective elements 6 wereformed, this hologram pattern being formed such that lightperpendicularly incident to that surface was diffused in thelongitudinal axial direction and shorter axial direction respectively at60° and 1°. The light guide plate 1 was arranged such that the face atthe reflective elements 6 side of the light guide plate 1 opposed theoptical sheet 8 and the face at the anisotropic diffusion patternintegrated layer 18 side of the light guide plate 1 opposed thereflector 10.

The optical sheet 8 was a prism film M165 by Mitsubishi Rayon, the prismface being disposed so as to oppose the side of the light guide plate 1.The reflector 10 was provided by a silver deposition of 1000 Å appliedto a variety of prism films, disposed such that the crest line directionwas orthogonal to the entry face 5.

For this first example, a reflector 10 of the first embodiment as thatshown in FIG. 4 having trapezoidal section prism elements formed with nogap therebetween was used, the base angle of the trapezoid being 45° andthe ratio of the flat part of the trapezoid being 0.15. Here, the ratioof the flat part means the proportion of a face of one side of thereflector 10 occupied by the area of the flat part. The luminance of thebacklight device according to this first example was 2290 (cd/m²), andwhen observed from the upper surface of the optical sheet 8, there wasno bright line in the region of the entry face 5 of the light guideplate 1.

For the second example, a reflector 10 of the first embodiment as thatshown in FIG. 4 having trapezoidal section prism elements formed with nogap therebetween was used, the base angle of the trapezoid being 45° andthe ratio of the flat part of the trapezoid being 0.11. The luminance ofthe backlight device according to this second example was 2225 (cd/M²),and when observed from the upper surface of the optical sheet 8, therewas no bright line in the region of the entry face 5 of the light guideplate 1.

For the third example, a reflector 10 of a second embodiment as thatshown in FIG. 5 having an iteration of trapezoidal section prismelements formed with gaps between the elements was used, the base angleof the trapezoid being 45° and the ratio of the flat part of thetrapezoid being 0.24. The luminance of the backlight device according tothis third example was 2320 (cd/M²), and when observed from the uppersurface of the optical sheet 8, there was no bright line in the regionof the entry face 5 of the light guide plate 1.

For the fourth example, a reflector 10 of the second embodiment as thatshown in FIG. 5 having an iteration of trapezoidal section prismelements formed with gaps therebetween was used, the base angle of thetrapezoid being 45° and the ratio of the flat part of the trapezoidbeing 0.41. The luminance of the backlight device according to thisfourth example was 2350 (cd/m²)), and when observed from the uppersurface of the optical sheet 8, there were subtle blight lines in theregion of the entry face 5 of the light guide plate 1.

Comparative examples will now be provided for the purpose of providing acontrast to the above described backlight device embodiments. In theseexamples the same configuration is used as that described with respectto the above examples unless specifically stated otherwise.

The first comparative example employs the reflector 10 according to thefirst embodiment as that shown in FIG. 4, having trapezoidal sectionprism elements formed with no gap therebetween, the base angle of thetrapezoid being 45° and the ratio of the flat part of the trapezoidbeing 0. The luminance of this backlight device of this firstcomparative example was 2100 (cd/m²), and when observed from the uppersurface of the optical sheet 8, there was no bright line in the regionof the entry face 5 of the light guide plate 1.

For the second comparative example, a reflector 10 of the firstembodiment as that shown in FIG. 4 having trapezoidal section prismelements formed with no gap therebetween was used, the base angle of thetrapezoid being 27° and the ratio of the flat part of the trapezoidbeing 0.30. The luminance of the backlight device according to thissecond comparative example was 2182 (cd/m²), and when observed from theupper surface of the optical sheet 8, there were bright lines in theregion of the entry face 5 of the light guide plate 1.

For the third comparative example a mirror surface shape reflector 10was used. The luminance of the backlight device according to this thirdcomparative example was 2360 (cd/m²), and when observed from the uppersurface of the optical sheet 8, darkness between the light sources andclear bright lines were observed in the region of the entry face 5 ofthe light guide plate 1.

Table 1 brings together the results of the above described embodimentsand the comparative examples.

Base Angle of Ratio of Appearance of Luminance Reflector Form TrapezoidFlat Part Entry Part (cd/m²) Example 1 First Embodiment 45° 0.15 ⊚ 2290(FIG. 4) Example 2 First Embodiment 45° 0.11 ⊚ 2225 (FIG. 4) Example 3Second Embodiment 45° 0.24 ⊚ 2320 (FIG. 5) Example 4 Second Embodiment45° 0.41 ◯ 2350 (FIG. 5) Comparative First Embodiment 45° 0 ⊚ 2100Example 1 (FIG. 4) Comparative First Embodiment 27° 0.30 Δ 2182 Example2 (FIG. 4) Comparative Mirror Surface — — X 2360 Example 3 Appearance ofEntry Part ⊚: No bright line ◯: Subtle bright lines Δ: Bright lines X:Clear bright lines and darkness between light sources

Although the invention has been described herein by reference to anexemplary embodiment, the invention is not limited thereby, andmodifications and variations of the embodiment as described will occurto those skilled in the art, in light of the above teachings. Further,the particular values provided in the above description are intended toprovide examples that are illustrative with respect to the invention andnot restrictive.

1. A backlight device comprising: (a) a light guide plate thatpropagates, reflects and diffuses light, disposed at a rear surface sideof a display device, wherein the light guide plate comprises (i) anentry face that light enters at one side of the light guide plate; (ii)an exit face disposed on a side of the light guide plate adjacent to aliquid crystal display device; and (iii) a lower face disposed opposingthe side of the light guide plate nearest to the liquid crystal displaydevice; (b) a light source disposed at least one end of the light guideplate; and (c) a reflector that comprises a structured face thatincludes an iteration of prism elements of trapezoidal section, a crestline direction of the prism elements being disposed orthogonally to theentry face of the light guide plate, wherein the reflector is disposedat the lower face of the light guide plate and reflects light from thelight guide plate at the structured face.
 2. The backlight deviceaccording to claim 1, wherein the light guide plate has reflectiveelements integratedly formed on the exit face, and the light guide plateemits light rays, by means of the reflective elements, in the directionof the reflector adjacent to the lower face of the light guide plate. 3.The backlight device according to claim 2, wherein an anisotropicdiffusion pattern is formed on the lower face of the light guide plate.4. The backlight device according to claim 2, wherein the reflectiveelements comprise V-shaped grooves, wherein an inclined face of thegrooves is directed to face light sources so that an angle ofinclination of the inclined face brings light from the entry facegradually to a first angle below a second angle for total internalreflection.
 5. The backlight device according to claim 2, wherein a rateof reflectivity of the reflector is not less than 75%, and a repetitioncycle of the prism elements is 1-200 μm, and an angle formed by anoblique side of the trapezoidal section and a base thereof is 20-70° anda ratio of the sum of a length of an upper side of the trapezoidalsection and a length of a gap between prism elements is a ratio in therange of 0.05-0.5 in relation to the repetition cycle of the prismelements.
 6. The backlight device according to claim 3, wherein thereflective elements comprise V-shaped grooves, wherein an inclined faceof the grooves is directed to face light sources so that an angle ofinclination of the inclined face brings light from the entry facegradually to a first angle below a second angle for total internalreflection.
 7. The backlight device according to claim 3, wherein a rateof reflectivity of the reflector is not less than 75%, and a repetitioncycle of the prism elements is 1-200 μm, and an angle formed by anoblique side of the trapezoidal section and a base thereof is 20-70° anda ratio of the sum of a length of an upper side of the trapezoidalsection and a length of a gap between prism elements is a ratio in therange of 0.05-0.5 in relation to the repetition cycle of the prismelements.
 8. The backlight device according to claim 6, wherein a rateof reflectivity of the reflector is not less than 75%, and a repetitioncycle of the prism elements is 1-200 μm, and an angle formed by anoblique side of the trapezoidal section and a base thereof is 20-70° anda ratio of the sum of a length of an upper side of the trapezoidalsection and a length of a gap between prism elements is a ratio in therange of 0.05-0.5 in relation to the repetition cycle of the prismelements.
 9. The backlight device according to claim 4, wherein a rateof reflectivity of the reflector is not less than 75%, and a repetitioncycle of the prism elements is 1-200 μm, and an angle formed by anoblique side of the trapezoidal section and a base thereof is 20-70° anda ratio of the sum of a length of an upper side of the trapezoidalsection and a length of a gap between prism elements is a ratio in therange of 0.05-0.5 in relation to the repetition cycle of the prismelements.
 10. The backlight device according to claim 1, wherein ananisotropic diffusion pattern is formed on the lower face of the lightguide plate.
 11. The backlight device according to claim 1, wherein arate of reflectivity of the reflector is not less than 75%, and arepetition cycle of the prism elements is 1-200 μm, and an angle formedby an oblique side of the trapezoidal section and a base thereof is20-70° and a ratio of the sum of a length of an upper side of thetrapezoidal section and a length of a gap between prism elements is aratio in the range of 0.05-0.5 in relation to the repetition cycle ofthe prism elements.
 12. The backlight device according to claim 10,wherein a rate of reflectivity of the reflector is not less than 75%,and a repetition cycle of the prism elements is 1-200 μm, and an angleformed by an oblique side of the trapezoidal section and a base thereofis 20-70° and a ratio of the sum of a length of an upper side of thetrapezoidal section and a length of a gap between prism elements is aratio in the range of 0.05-0.5 in relation to the repetition cycle ofthe prism elements.
 13. The backlight device according to claim 1,wherein a height of the trapezoidal section of prism elements isconstant.
 14. The backlight device according to claim 1, wherein aheight of the trapezoidal section of prism elements is progressivelydecreasing.
 15. The backlight device according to claim 1, furthercomprising: (d) an optical sheet disposed above the exit face of thelight guide plate, wherein the optical sheet has a flat upper face and alower face, and wherein reflective grooves forming a continuousprism-shaped construction are disposed on the lower face of the opticalsheet.
 16. The backlight device according to claim 1, wherein the prismelements comprise a variety of prism films.